Pressure sensitive adhesives (PSAs) are known to possess properties including the following: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend or substrate, and (4) sufficient cohesive strength to be removed cleanly from the adherend. Materials that have been found to function well as PSAs include polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear holding power. PSAs are characterized by being normally tacky at room temperature (e.g., 20° C.). PSAs do not embrace compositions merely because they are sticky or adhere to a surface.
Only a limited number of classes of polymers have been found to function as PSAs. Among these polymer classes are natural and synthetic rubbers, (meth)acrylic polymers, silicones, block copolymers and olefins. Acrylic polymers have proven especially useful. Acrylic based PSAs are frequently prepared from isooctyl acrylate or 2-ethylhexyl acrylate. These adhesives have many desirable attributes such as high peel adhesion when applied to a wide variety of surfaces. Acrylic PSAs, however, do not typically provide high thermal stability and will slowly degrade upon exposure to higher temperature (e.g., above 125° C.). Thermal degradation of these known acrylic adhesives at higher temperatures reduces the cohesive strength of the adhesive and may generate bubble formation from high levels of outgassing, resulting in a loss of adhesion. It is desirable to provide silicone-free PSAs that will strongly adhere to surfaces at temperatures up to at least about 175° C. or even higher temperatures.
Further, acryclic PSAs are generally derived from petroleum feedstocks. The increase in the price of oil, and concomitant petroleum-derived products, has led to volatile prices and supply for many adhesive products. It is desirable to replace all or part of the petroleum-based feedstocks with those derived from renewable sources, such as plants, as such materials become relatively cheaper, and are therefore both economically and socially beneficial. Therefore, the need for such plant-derived materials has become increasingly significant.